(1) Field of the Invention
The present invention generally relates to battery charging systems. More specifically, the present invention relates to a battery charging system and method for identifying the type of battery pack and charging the battery pack accordingly.
(2) Description of the Related Art
In the past, portable, battery-operated electric and electronic equipment were typically powered by primary batteries which are non-rechargeable batteries that had to be disposed of after a single use. However, as small, maintenance-free rechargeable batteries (also known in the art as "secondary" batteries) have been developed, these secondary batteries have become the battery of choice for many applications. Secondary batteries afford a lower life-cycle cost as they can be recharged and reused and offer the convenience of using a replaceable cell over a one-time-use cell. Secondary batteries are being used in increasing numbers to power portable equipment such as tools, toys, lighting, photographic, radio, and, more significantly, consumer electronic devices such as laptop computers, camcorders, cellular phones, and bar code readers.
Secondary batteries come in different chemistries (e.g., NiCd, Alkaline, Lithium Ion (Li-Ion), Nickel Metal Hydride (NiMH), sizes, and shapes. Different batteries also have different charging parameters. A battery charger which accepts different battery types should adapt its charging parameters in accordance with the battery type detected. However, proper recharging is critical since it is important that the battery not be overcharged or undercharged.
Overcharge can cause the battery to run at high temperatures and rupture, thereby destroying the battery. Further the battery acid and electrolyte that leak can damage the equipment that houses the battery. Lithium based chemistries are particularly sensitive to voltage and so it is important that these batteries be charged with the proper voltage. In extreme cases, the battery can explode causing physical harm. At a minimum, overcharging can greatly shorten the battery life thereby reducing the effective life of the battery.
Undercharge can also shorten the effective life of the battery. The duration of the battery charge is not fully utilized since the amount of charge that can be stored in the battery is not at a maximum capacity.
Prior art battery chargers have the ability to sense the different required charging rates for batteries having different capacities so as to supply the appropriate charge parameters. An example of a battery charging system is one that includes a charger apparatus and a battery which employs a sense resistor, within the battery housing itself. The sense resistor provides an electrical signature indication of battery type and charge state. Based upon the battery type detected, charge control circuitry in the charger apparatus adapts its charging parameters accordingly.
Prior art battery chargers have several drawbacks, however. The resistor within the battery can open or short and the resistive value may change over time, thereby causing erroneous readings. For example, if a resistor value of 1 k is one charge level and 1.1 k is a second charge level, over time, a 1 k resistor can move closer to 1.1 k and a 1.1 k resistor can move closer to 1 k thereby causing incorrect results.
Further, once the resistor value is predetermined or fixed, it is static and cannot be changed. During manufacturing, many options are available to assign different resistor values to different battery types and charge levels. But once the value is set, the battery type cannot be changed. The batteries would need to be recalled by the battery manufacturer and the resistors replaced with new values.
Additionally, several components are required in the prior art battery charging system. A sense resistor is needed in the battery. A third contact terminal for the sense resistor (in addition to the "+" terminal and the "-" terminal) is also required. In addition, circuitry for detecting the resistor must be installed in the battery charger. These additional components all add cost, design, and manufacturing complexity to the overall battery charging system.
Finally, prior art battery chargers are typically designed to charge only new battery types and are generally not compatible with older, previous generation batteries. It would be desirable to have a single battery charger that can accommodate both new and older batteries so that the older batteries do not have to be discarded, space can be saved, and ease of use can be enhanced.
Therefore, it is desirable to provide a simple and cost-efficient battery charger to automatically recognize the battery type which is to be charged and to adapt its charging parameters accordingly.